title: Intramuscular fat in the longissimus muscle is reduced in lambs from sires selected for leanness.
abstract: Selection for lean growth through Australian Sheep Breeding Values (ASBVs) for post weaning weight (PWWT), eye muscle depth (PEMD) and c-site fat depth (PFAT) raises concerns regarding declining intramuscular fat (IMF) levels. Reducing PFAT decreased IMF by 0.84% for Terminal sired lambs. PEMD decreased IMF by 0.18% across all sire types. Female lambs had higher IMF levels and this was unexplained by total carcass fatness. The negative phenotypic association between measures of muscling (shortloin muscle weight, eye muscle area) and IMF, and positive association between fatness and IMF, was consistent with other literature. Hot carcass weight increased IMF by 2.08% between 12 and 40 kg, reflective of development of IMF as lambs approach maturity. Selection objectives with low PFAT sires will reduce IMF, however the lower impact of PEMD and absence of a PWWT effect, will enable continued selection for lean growth without influencing IMF. Alternatively, the negative impact of PFAT could be off-set by inclusion of an IMF ASBV.
authors.affiliation: Australian Cooperative Research Centre for Sheep Industry Innovation, Australia; Murdoch University, School of Veterinary & Life Sciences, Western Australia 6150, Australia. Electronic address: l.pannier@murdoch.edu.au.
authors.forename: L
authors.initials: L
authors.lastname: Pannier
authors.forename: D W
authors.initials: DW
authors.lastname: Pethick
authors.forename: G H
authors.initials: GH
authors.lastname: Geesink
authors.forename: A J
authors.initials: AJ
authors.lastname: Ball
authors.forename: R H
authors.initials: RH
authors.lastname: Jacob
authors.forename: G E
authors.initials: GE
authors.lastname: Gardner
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism*; D050154:Adiposity / Q000235:genetics*; D000818:Animals; D001315:Australia; D001947:Breeding; D004032:Diet; D005123:Eye; D006128:Growth / Q000235:genetics; D006801:Humans; D008460:Meat / Q000032:analysis*; D009132:Muscles / Q000378:metabolism*; D009929:Organ Size; D064170:Paraspinal Muscles / Q000378:metabolism*; D034561:Sheep, Domestic / Q000235:genetics; D014886:Weaning; D015430:Weight Gain / Q000235:genetics*
keywords: Breeding value; Fatness; Intramuscular fat; Lamb; Muscling